Shane Reynolds balk

[Jay R]

Anyone see the Braves-Mets game tonight? Shane Reynolds was called with a balk. There was a runner on third and Reynolds was pitching from the windup. He was on the rubber and stepped back with his left foot first. The announcers said that was the reason for the balk because it looked like he was starting his delivery. When you step off the rubber, does it matter with which foot? I'm wondering if it wasn't something else.